That really only applies to some specific romance plots. I'm far from an expert in romance fiction, but I hope I'm at least well-read enough to have at least some clue about its various forms and variations. And romance and loving relationships can be treated in several different ways in fiction.
The most common form of romance, and arguably the dominant form where the romance is the main plot, is where the question is if the couple will get together or not in the end—the conclusion is a kiss, or an engagement, or a marriage, or the birth of a child (as Lois Bujold once said the "birth of a child is the proper climax, after all, of any romance that starts out “boy meets girl,” if the romance is not falsely truncated"). And there you can either have internal or external factors as the obstacles or objections to overcome to reach the happy ending. But there are several other forms that the matter of love and loving relationships can take in fiction.
Which partner? Here we get the classic triangle drama, but again, this is largely a variation of the "boy meets girl". This was the path chosen for Clark Kent–Lois Lane–Superman, and was also a complicating element for Diana Prince–Steve Trevor–Wonder Woman.
Partners in adventure, where the couple is established (and might be either platonic or sexual), and they together overcome obstacles, and sometimes have conflicts (in different ways) over how they are to overcome the various obstacles. Xena and Gabrielle is an excellent example,
Valérian and Laureline is another. Note here that the latter very often place the two acting independently, often on different facets of the same mission, but sometimes on entirely different missions.
Domestic life, where the focus is on home life and things happening with their friends. Perhaps not that well suited to a superhero comics, but it can and likely should be used as seasoning. Think of "The Cosby Show".
But I think that any attempt to build a great relationship between the two must take some effort to tell Steve's story in some way, like the movie or "The Legend of Wonder Woman" did. But in most other cases, he's mostly there as a support and enabler for Diana, he has little or no independent role in the stories.
ETA: Exchanged "Etta" for "Diana" in the last sentence, due to not thinking while typing.